/**
 *
 * Copyright (c) 2014, the Railo Company Ltd. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either 
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public 
 * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 * 
 **/
package lucee.runtime.net.ntp;

import java.text.DecimalFormat;
import java.util.Date;
import java.util.concurrent.ThreadLocalRandom;

import lucee.commons.i18n.DateFormatPool;

public final class NtpMessage {
	/**
	 * This is a two-bit code warning of an impending leap second to be inserted/deleted in the last
	 * minute of the current day. It's values may be as follows:
	 * 
	 * Value Meaning ----- ------- 0 no warning 1 last minute has 61 seconds 2 last minute has 59
	 * seconds) 3 alarm condition (clock not synchronized)
	 */
	public byte leapIndicator = 0;

	/**
	 * This value indicates the NTP/SNTP version number. The version number is 3 for Version 3 (IPv4
	 * only) and 4 for Version 4 (IPv4, IPv6 and OSI). If necessary to distinguish between IPv4, IPv6
	 * and OSI, the encapsulating context must be inspected.
	 */
	public byte version = 3;

	/**
	 * This value indicates the mode, with values defined as follows:
	 * 
	 * Mode Meaning ---- ------- 0 reserved 1 symmetric active 2 symmetric passive 3 client 4 server 5
	 * broadcast 6 reserved for NTP control message 7 reserved for private use
	 * 
	 * In unicast and anycast modes, the client sets this field to 3 (client) in the request and the
	 * server sets it to 4 (server) in the reply. In multicast mode, the server sets this field to 5
	 * (broadcast).
	 */
	public byte mode = 0;

	/**
	 * This value indicates the stratum level of the local clock, with values defined as follows:
	 * 
	 * Stratum Meaning ---------------------------------------------- 0 unspecified or unavailable 1
	 * primary reference (e.g., radio clock) 2-15 secondary reference (via NTP or SNTP) 16-255 reserved
	 */
	public short stratum = 0;

	/**
	 * This value indicates the maximum interval between successive messages, in seconds to the nearest
	 * power of two. The values that can appear in this field presently range from 4 (16 s) to 14 (16284
	 * s); however, most applications use only the sub-range 6 (64 s) to 10 (1024 s).
	 */
	public byte pollInterval = 0;

	/**
	 * This value indicates the precision of the local clock, in seconds to the nearest power of two.
	 * The values that normally appear in this field\ range from -6 for mains-frequency clocks to -20
	 * for microsecond clocks found in some workstations.
	 */
	public byte precision = 0;

	/**
	 * This value indicates the total roundtrip delay to the primary reference source, in seconds. Note
	 * that this variable can take on both positive and negative values, depending on the relative time
	 * and frequency offsets. The values that normally appear in this field range from negative values
	 * of a few milliseconds to positive values of several hundred milliseconds.
	 */
	public double rootDelay = 0;

	/**
	 * This value indicates the nominal error relative to the primary reference source, in seconds. The
	 * values that normally appear in this field range from 0 to several hundred milliseconds.
	 */
	public double rootDispersion = 0;

	/**
	 * This is a 4-byte array identifying the particular reference source. In the case of NTP Version 3
	 * or Version 4 stratum-0 (unspecified) or stratum-1 (primary) servers, this is a four-character
	 * ASCII string, left justified and zero padded to 32 bits. In NTP Version 3 secondary servers, this
	 * is the 32-bit IPv4 address of the reference source. In NTP Version 4 secondary servers, this is
	 * the low order 32 bits of the latest transmit timestamp of the reference source. NTP primary
	 * (stratum 1) servers should set this field to a code identifying the external reference source
	 * according to the following list. If the external reference is one of those listed, the associated
	 * code should be used. Codes for sources not listed can be contrived as appropriate.
	 * 
	 * Code External Reference Source ---- ------------------------- LOCL uncalibrated local clock used
	 * as a primary reference for a subnet without external means of synchronization PPS atomic clock or
	 * other pulse-per-second source individually calibrated to national standards ACTS NIST dialup
	 * modem service USNO USNO modem service PTB PTB (Germany) modem service TDF Allouis (France) Radio
	 * 164 kHz DCF Mainflingen (Germany) Radio 77.5 kHz MSF Rugby (UK) Radio 60 kHz WWV Ft. Collins (US)
	 * Radio 2.5, 5, 10, 15, 20 MHz WWVB Boulder (US) Radio 60 kHz WWVH Kaui Hawaii (US) Radio 2.5, 5,
	 * 10, 15 MHz CHU Ottawa (Canada) Radio 3330, 7335, 14670 kHz LORC LORAN-C radionavigation system
	 * OMEG OMEGA radionavigation system GPS Global Positioning Service GOES Geostationary Orbit
	 * Environment Satellite
	 */
	public byte[] referenceIdentifier = { 0, 0, 0, 0 };

	/**
	 * This is the time at which the local clock was last set or corrected, in seconds since 00:00
	 * 1-Jan-1900.
	 */
	public double referenceTimestamp = 0;

	/**
	 * This is the time at which the request departed the client for the server, in seconds since 00:00
	 * 1-Jan-1900.
	 */
	public double originateTimestamp = 0;

	/**
	 * This is the time at which the request arrived at the server, in seconds since 00:00 1-Jan-1900.
	 */
	public double receiveTimestamp = 0;

	/**
	 * This is the time at which the reply departed the server for the client, in seconds since 00:00
	 * 1-Jan-1900.
	 */
	public double transmitTimestamp = 0;

	/**
	 * Constructs a new NtpMessage from an array of bytes.
	 * 
	 * @param array
	 */
	public NtpMessage(byte[] array) {
		// See the packet format diagram in RFC 2030 for details
		leapIndicator = (byte) ((array[0] >> 6) & 0x3);
		version = (byte) ((array[0] >> 3) & 0x7);
		mode = (byte) (array[0] & 0x7);
		stratum = unsignedByteToShort(array[1]);
		pollInterval = array[2];
		precision = array[3];

		rootDelay = (array[4] * 256.0) + unsignedByteToShort(array[5]) + (unsignedByteToShort(array[6]) / 256.0) + (unsignedByteToShort(array[7]) / 65536.0);

		rootDispersion = (unsignedByteToShort(array[8]) * 256.0) + unsignedByteToShort(array[9]) + (unsignedByteToShort(array[10]) / 256.0)
				+ (unsignedByteToShort(array[11]) / 65536.0);

		referenceIdentifier[0] = array[12];
		referenceIdentifier[1] = array[13];
		referenceIdentifier[2] = array[14];
		referenceIdentifier[3] = array[15];

		referenceTimestamp = decodeTimestamp(array, 16);
		originateTimestamp = decodeTimestamp(array, 24);
		receiveTimestamp = decodeTimestamp(array, 32);
		transmitTimestamp = decodeTimestamp(array, 40);
	}

	/**
	 * Constructs a new NtpMessage
	 * 
	 * @param leapIndicator
	 * @param version
	 * @param mode
	 * @param stratum
	 * @param pollInterval
	 * @param precision
	 * @param rootDelay
	 * @param rootDispersion
	 * @param referenceIdentifier
	 * @param referenceTimestamp
	 * @param originateTimestamp
	 * @param receiveTimestamp
	 * @param transmitTimestamp
	 */
	public NtpMessage(byte leapIndicator, byte version, byte mode, short stratum, byte pollInterval, byte precision, double rootDelay, double rootDispersion,
			byte[] referenceIdentifier, double referenceTimestamp, double originateTimestamp, double receiveTimestamp, double transmitTimestamp) {
		// ToDo: Validity checking
		this.leapIndicator = leapIndicator;
		this.version = version;
		this.mode = mode;
		this.stratum = stratum;
		this.pollInterval = pollInterval;
		this.precision = precision;
		this.rootDelay = rootDelay;
		this.rootDispersion = rootDispersion;
		this.referenceIdentifier = referenceIdentifier;
		this.referenceTimestamp = referenceTimestamp;
		this.originateTimestamp = originateTimestamp;
		this.receiveTimestamp = receiveTimestamp;
		this.transmitTimestamp = transmitTimestamp;
	}

	/**
	 * Constructs a new NtpMessage in client -> server mode, and sets the transmit timestamp to the
	 * current time.
	 */
	public NtpMessage() {
		// Note that all the other member variables are already set with
		// appropriate default values.
		this.mode = 3;
		this.transmitTimestamp = (System.currentTimeMillis() / 1000.0) + 2208988800.0;
	}

	/**
	 * This method constructs the data bytes of a raw NTP packet.
	 * 
	 * @return
	 */
	public byte[] toByteArray() {
		// All bytes are automatically set to 0
		byte[] p = new byte[48];

		p[0] = (byte) (leapIndicator << 6 | version << 3 | mode);
		p[1] = (byte) stratum;
		p[2] = pollInterval;
		p[3] = precision;

		// root delay is a signed 16.16-bit FP, in Java an int is 32-bits
		int l = (int) (rootDelay * 65536.0);
		p[4] = (byte) ((l >> 24) & 0xFF);
		p[5] = (byte) ((l >> 16) & 0xFF);
		p[6] = (byte) ((l >> 8) & 0xFF);
		p[7] = (byte) (l & 0xFF);

		// root dispersion is an unsigned 16.16-bit FP, in Java there are no
		// unsigned primitive types, so we use a long which is 64-bits
		long ul = (long) (rootDispersion * 65536.0);
		p[8] = (byte) ((ul >> 24) & 0xFF);
		p[9] = (byte) ((ul >> 16) & 0xFF);
		p[10] = (byte) ((ul >> 8) & 0xFF);
		p[11] = (byte) (ul & 0xFF);

		p[12] = referenceIdentifier[0];
		p[13] = referenceIdentifier[1];
		p[14] = referenceIdentifier[2];
		p[15] = referenceIdentifier[3];

		encodeTimestamp(p, 16, referenceTimestamp);
		encodeTimestamp(p, 24, originateTimestamp);
		encodeTimestamp(p, 32, receiveTimestamp);
		encodeTimestamp(p, 40, transmitTimestamp);

		return p;
	}

	/**
	 * Returns a string representation of a NtpMessage
	 * 
	 * @return
	 */
	@Override
	public String toString() {
		String precisionStr = new DecimalFormat("0.#E0").format(Math.pow(2, precision));
		return "Leap indicator: " + leapIndicator + "\n" + "Version: " + version + "\n" + "Mode: " + mode + "\n" + "Stratum: " + stratum + "\n" + "Poll: " + pollInterval + "\n"
				+ "Precision: " + precision + " (" + precisionStr + " seconds)\n" + "Root delay: " + new DecimalFormat("0.00").format(rootDelay * 1000) + " ms\n"
				+ "Root dispersion: " + new DecimalFormat("0.00").format(rootDispersion * 1000) + " ms\n" + "Reference identifier: "
				+ referenceIdentifierToString(referenceIdentifier, stratum, version) + "\n" + "Reference timestamp: " + timestampToString(referenceTimestamp) + "\n"
				+ "Originate timestamp: " + timestampToString(originateTimestamp) + "\n" + "Receive timestamp:   " + timestampToString(receiveTimestamp) + "\n"
				+ "Transmit timestamp:  " + timestampToString(transmitTimestamp);
	}

	/**
	 * Converts an unsigned byte to a short. By default, Java assumes that a byte is signed.
	 * 
	 * @param b
	 * @return
	 */
	public static short unsignedByteToShort(byte b) {
		if ((b & 0x80) == 0x80) return (short) (128 + (b & 0x7f));
		return b;
	}

	/**
	 * Will read 8 bytes of a message beginning at <code>pointer</code> and return it as a double,
	 * according to the NTP 64-bit timestamp format.
	 * 
	 * @param array
	 * @param pointer
	 * @return
	 */
	public static double decodeTimestamp(byte[] array, int pointer) {
		double r = 0.0;

		for (int i = 0; i < 8; i++) {
			r += unsignedByteToShort(array[pointer + i]) * Math.pow(2, (3 - i) * 8);
		}

		return r;
	}

	/**
	 * Encodes a timestamp in the specified position in the message
	 * 
	 * @param array
	 * @param pointer
	 * @param timestamp
	 */
	public static void encodeTimestamp(byte[] array, int pointer, double timestamp) {
		// Converts a double into a 64-bit fixed point
		for (int i = 0; i < 8; i++) {
			// 2^24, 2^16, 2^8, .. 2^-32
			double base = Math.pow(2, (3 - i) * 8);

			// Capture byte value
			array[pointer + i] = (byte) (timestamp / base);

			// Subtract captured value from remaining total
			timestamp = timestamp - (unsignedByteToShort(array[pointer + i]) * base);
		}

		// From RFC 2030: It is advisable to fill the non-significan't
		// low order bits of the timestamp with a random, unbiased
		// bitstring, both to avoid systematic roundoff errors and as
		// a means of loop detection and replay detection.
		array[7] = (byte) ThreadLocalRandom.current().nextInt(256);
	}

	/**
	 * Returns a timestamp (number of seconds since 00:00 1-Jan-1900) as a formatted date/time string.
	 * 
	 * @param timestamp
	 * @return
	 */
	public static String timestampToString(double timestamp) {
		if (timestamp == 0) return "0";

		// timestamp is relative to 1900, utc is used by Java and is relative
		// to 1970
		double utc = timestamp - (2208988800.0);

		// milliseconds
		long ms = (long) (utc * 1000.0);

		// date/time
		String date = DateFormatPool.format("dd-MMM-yyyy HH:mm:ss", new Date(ms));

		// fraction
		double fraction = timestamp - ((long) timestamp);
		String fractionSting = new DecimalFormat(".000000").format(fraction);

		return date + fractionSting;
	}

	/**
	 * Returns a string representation of a reference identifier according to the rules set out in RFC
	 * 2030.
	 * 
	 * @param ref
	 * @param stratum
	 * @param version
	 * @return
	 */
	public static String referenceIdentifierToString(byte[] ref, short stratum, byte version) {
		// From the RFC 2030:
		// In the case of NTP Version 3 or Version 4 stratum-0 (unspecified)
		// or stratum-1 (primary) servers, this is a four-character ASCII
		// string, left justified and zero padded to 32 bits.
		if (stratum == 0 || stratum == 1) {
			return new String(ref);
		}

		// In NTP Version 3 secondary servers, this is the 32-bit IPv4
		// address of the reference source.
		else if (version == 3) {
			return unsignedByteToShort(ref[0]) + "." + unsignedByteToShort(ref[1]) + "." + unsignedByteToShort(ref[2]) + "." + unsignedByteToShort(ref[3]);
		}

		// In NTP Version 4 secondary servers, this is the low order 32 bits
		// of the latest transmit timestamp of the reference source.
		else if (version == 4) {
			return "" + ((unsignedByteToShort(ref[0]) / 256.0) + (unsignedByteToShort(ref[1]) / 65536.0) + (unsignedByteToShort(ref[2]) / 16777216.0)
					+ (unsignedByteToShort(ref[3]) / 4294967296.0));
		}

		return "";
	}
}